A turning tool or milling tool includes one or a plurality of indexable cutting inserts. As shown in FIG. 1, such an indexable cutting insert 1 has a face 2 present on the side where a cutting chip 6 of a work piece 5 is raised during cutting, and a flank 3 present on the side facing the work piece, the face 2 and the flank 3 being connected with an edge line 4 disposed therebetween, and the edge line 4 serving as a central point of an action of cutting the work piece 5.
When the indexable cutting insert reaches its tool life, it must be exchanged. In this case, when a insert has only one edge line, the insert itself must be exchanged. However, an indexable cutting insert having a plurality of edge lines can be turned several times on the same bearing surface so that an unused edge line is positioned at a cutting position, and thus the cutting insert can be used at a cutting position different from the previously used cutting position. In some cases, an unused edge line is attached to another bearing surface so that the edge line can be used.
However, at a cutting work site, an indexable cutting insert with an unused edge line may be exchanged or turned. This is due to the fact that when the edge is replaced or the edge line is turned, it is not recognized whether the edge line has been used or not. Therefore, this operation must be performed after whether the edge line has been unused or not is sufficiently recognized.
As a method for easily identifying a used edge line, an indexable cutting insert has been proposed, in which a flank and a face have different colors (Japanese Unexamined Patent Application Publication No. 2002-144108 (Patent Document 1)). Specifically, the indexable cutting insert includes a wear-resistant base layer formed on a body and referred to as a wear-reducing coating film, and a use-state indicating layer formed on the flank and composed of an easily wearing material.
Although such an indexable cutting insert having the above-mentioned constitution has an action of calling attention to whether the edge line has been used or not, the use-state indicating layer formed on the flank is readily welded to a work piece. There is thus the problem that the use-state indicating layer is welded to the surface of the work piece, and the cutting edge having unevenness due to welding of the work piece to the use-state indicating layer is used for a cutting work, thereby impairing the appearance and surface smoothness of the work piece after cutting.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-144108